Tony Blair failed to tell two of his most senior cabinet colleagues about secret plans to include the Lockerbie bomber in a prisoner-for-trade deal with Libya, Alex Salmond has suggested.

The first minister suggested that Lord Falconer, one of Blair's most trusted political friends, and Jack Straw, the justice secretary, believed that the UK would block Libya's demands for Abdelbaset al-Megrahi to be included in a new prisoner transfer treaty.

But the ministers were not "in the loop" with Blair's plans to include Megrahi in that treaty in his controversial "deal in the desert" with Muammar Gaddafi in May 2007 – plans that were eventually agreed with the Libyans by Gordon Brown in December 2007.

Salmond today told the Scottish affairs select committee at the Commons that, throughout the summer of 2007, Falconer and Straw had repeatedly reassured the Scottish government, both in letters and in face-to-face meetings, that Megrahi would be excluded from the treaty.

Salmond told the committee that the Scottish nationalist government in Edinburgh had consistently opposed the proposal to allow Megrahi to be included.

Salmond said that Falconer, who was justice secretary until Blair stood down in June 2007, had "explicitly said: 'This isn't a difficulty. We've told the Libyans that Megrahi won't be included,' and Jack Straw in July of that year said quite openly that he didn't see any great difficulty, they would just negotiate a PTA [prisoner transfer agreement] which would give us the assurances we desired."

Salmond believed that transferring Megrahi to Libya before his 26-year life sentence was over would breach an undertaking to the US government and US relatives before Megrahi's trial that the Libyan would remain in a Scottish jail.

But in December 2007, after Gordon Brown had become prime minister, the UK government reneged on that position and, Salmond alleged, the deal with the US, when it revealed that the prisoner transfer agreement did not exclude Megrahi.

Straw was forced to say the government now believed it was in the UK's "overwhelming national interests", claiming that the UK's business dealings, security and its desire to see Libya re-enter the international community, overrode Scotland's objections.

Salmond said there was "again an 'evolution' in the UK government's position over this period".

He told the committee, which is investigating inter-government relations between Edinburgh and London, that the prisoner treaty was wrong. "It was a mistake because it raised an expectation by the Libyan government that Mr Megrahi would be included in such a prisoner transfer," he said.

"It was a mistake because it cut across the due process of Scots law, because one of the provisions of prisoner transfer is that legal proceedings would have to come to an end.

"It was a mistake because it was cut across what we believe to be prior agreements with the United States government and the relatives."

Giving evidence immediately after Salmond, the Scottish justice secretary, Kenny MacAskill, told the committee he had no regrets about his decision to release Megrahi on compassionate grounds, as he is dying from terminal cancer.

"We followed the rules and guidance. We believe we came to the right decision for the right reasons," he said.